1. Field of the Invention
The present invention relates to a method and a device for inspecting thin films which are widely employed in a semiconductor manufacturing process, and more particularly to a method and a device for inspecting thin films wherein the surfaces of the thin films are inspected using an optical interference phenomenon, thereby allowing the inspection irrespective of the kind of film.
2. Description of the Related Art
Thin-film inspection is very important in manufacturing products such as LCD and PDP that use semiconductor processing mainly composed of processes of deposition, exposure, and etching. In the case of TFT LCD, thin films with thicknesses less than 1000 Å are piled up to form a pattern. Presence/absence and shortage/excess of the pattern or contamination by foreign substances have a serious influence on the resulting product. Accordingly, it is necessary to inspect the thin film for forming the pattern. As semiconductor processing methods have developed, various methods of inspection have been proposed. Most of the inspection methods can be classified into several types as follows.
Among them, the most general method is an inspection method that uses an optical system including a CCD 11 and an illuminator 12 a shown in FIG. 1. In this method, light from the illuminator 12 is uniformly illuminated from various incident angles to an inspection target 10, and thereby images of the inspection target are obtained, not depending on the change of the thickness of the inspection target, a scratch or a minute projection thereon. Generally, this method is used to perform two-dimensional measurement of the pattern, rather than to inspect the pattern. It is general to use a LED as a light source in order to provide uniform and wide range of illumination.
However, this optical system is not suitable for detecting minute defects or determining inspection conditions on the pattern, or for performing a high-speed inspection using a linear CCD because an illuminator suitable for an area CCD is used.
In addition, there is an inspection method using a coaxial incident illumination. In this method, as shown in FIG. 2, a coaxial incident illuminator 21 and an inclined illuminator 22 are fixed at appropriate disposition-angles to illuminate light to the surface of an inspection target 20 so as to obtain an image thereof via a CCD 23.
When this method is used, optimal inspection conditions closely depend on the characteristics of the thin-film pattern, but it is very difficult to adjust these conditions. The only adjustable inspection-condition is the brightness of the coaxial and inclined illuminators. Therefore, when there are different kinds of patterns, or the characteristics of the pattern are changed, the optimal inspection condition cannot be obtained. In addition, even in the same process, it is necessary to adjust inspection conditions in response to different process conditions. This inspection method cannot meet such needs.
Further, Orbotech co. proposed a thin-film inspection method that uses an optics technology called “Ellipsometry”. This method was disclosed in U.S. Pat. No. 5,333,052. An inspection device used in this method includes a polarizer 31, a retardation plate 32, and an analyzer 33. Light emitted from an illuminator 35 is linearly polarized through the polarizer 31 and irradiated to the surface of an inspection target 30. Elliptically-polarized light reflected from the inspection target 30 is linearly polarized again through the analyzer 32. Thereafter, the linearly-polarized light is incident on a CCD sensor 34 whereby an image of the inspection target is obtained. As a result, this method has an advantage in that the inspection sensitivity is maximized for a particular type of film, and the brightness of a thin film can be adjusted for emphasis of the thin film by changing the rotation angles of the retardation plate and analyzer.
That is, this inspection method has an advantage in that because the brightness can be adjusted by changing the rotation angles of the retardation plate 32 and the analyzer 33, inspection conditions can be changed according to the characteristics of the film. However, when there are two or more films having different properties, this method cannot determine one inspection condition suitable for all the various kinds of properties of films. As a result, if inspection conditions for a specific thin film are optimized, inspection conditions for a different thin film are degraded.
Consequently, the prior art thin-film inspection methods have problems that it is difficult to set an inspection condition when there are various kinds of thin films, and therefore their optimal inspection conditions become different under a particular condition, lowering the reliability of the inspection result.
That is, the prior art thin-film inspection methods use one illuminator, or various kinds of light sources at the same time as needed for inspecting the surface of the inspection target to meet a specific requirement, or use an old optical instrument such as Ellipsometry for the inspection. However, the prior arts are very difficult to increase the relative sensitivity between patterns, and do not have an appropriate adjustment method for heterogeneous patterns.